1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus using the zoom lens, in particular, a three-unit zoom lens suitable for compact cameras, which is small sized, has a high zoom ratio and has a wide angle of view.
2. Description of the Related Art
Conventionally, as a zoom lens for compact cameras, a two-unit zoom lens with simple composition has been widely used. However, in the zoom lens for compact cameras, demands for miniaturization and high zoom ratio have been increased in recent years.
Especially on the occasion of zooming, a demand for making a wide field angle at a short focal length end is increasing. For this purpose, in a two-unit zoom lens with simple composition, there is a limit in obtaining a balance of good aberration from the short focal length end to a long focal length end, and accordingly a three-unit zoom lens has been widely used.
Furthermore, a telephoto-type lens system in which the last lens group has negative composition has been widely used, because it has merits that necessity to keep a long back focus is low and the total length of the lens system can be shortened in the lens system for compact cameras, which is different from the case of a lens system for single-lens reflex cameras.
Especially, in a three-unit zoom lens, positive-positive-negative lens composition is widely used since it is effective for shortening the total length of the lens system at the long focal length end.
As such examples, a small-sized zoom lens having high zoom ratio has been proposed in Publications of Unexamined Patent Application of Japan, such as Toku Kai No. 2002-258158, Toku Kai No.2000-66103, Toku Kai Hei No.11-295600, Toku Kai Hei No. 11-52232, Toku Kai No. 2002-98894, the specification of the U.S. Pat. No. 6,236,515 and the like.